The present invention relates to a paper feeding roller for use with a printer, and more particularly, to a rotation propagating system, based on manual operation, for rotationally driving a paper feeding roller.
A printer is typically equipped with a paper feeding mechanism for feeding sheets of paper in a column-direction orthogonal to a printing-row-direction along a front surface of a platen. This paper feeding mechanism is typically composed of a paper feeding roller disposed in the middle of a paper feeding passageway leading from a paper insertion port of a casing via a front surface of the platen to a discharge port, a friction roller so supported on the paper feeding roller as to be press-fittable thereto and releasable therefrom, and a driving system for rotationally driving the paper feeding roller. This driving system incorporates a deceleration gear mechanism for feeding the paper by transferring a driving force of a motor to rotate the paper feeding roller, or alternatively by manually rotating the paper feeding roller.
According to the prior art, this type of paper feeding mechanism has a construction illustrated, e.g., in FIG. 5. The casing 1 of the printer body encases a base frame 2 mounted with a printing mechanism unit constituting the printer and a paper feeding unit. The frame 2 includes a pair of side frames 2a and 2b which stand erect bilaterally and are parallely disposed at a given spacing. A platen (not illustrated) is supported between the side frames 2a and 2b. The printing mechanism unit (not shown) is placed in front of the platen, while the paper feeding mechanism unit is disposed in back of the platen.
A paper feeding roller 3 is rotatably supported between the side frames 2a and 2b. A friction roller 4 is supported in one radial direction of the paper feeding roller 3 so that the friction roller 4 is freely rotatable and movable in the radial direction. The friction roller 4 is press-fitted to the paper feeding roller 3 by the biasing force of a spring.
The side frame 2a is fitted with a stepper motor 5 intended to feed the paper. A small diameter gear 6 of a first stage is mounted on the driving shaft of the stepper motor 5. A large diameter gear 6b of a second stage and a small diameter gear 6c of a third stage are rotatably coaxially mounted on the side frame 2a. The first stage gear 6a meshes with the large diameter gear 6b. The large diameter gear 6b meshes with the small diameter gear 6c. The paper feeding roller 2 is equipped with a large diameter gear 6d of a final stage. The final stage gear 6d engages the third stage gear 6c. A gear train is formed of the gears 6a through 6d. A deceleration gear system 6 having a specified deceleration ration is thus constructed.
The paper feeding roller 3 is rotated through the deceleration gear system 6 by the driving force of the stepper motor 5. The rotation of this paper feeding roller 3 permits the feeding of the paper sandwiched in between the paper feeding roller 3 and the friction roller 4 along a predetermined paper feeding passageway. The paper passing between the paper feeding roller 3 and the friction roller 4 is fed via the front surface of the platen to a paper discharge port provided at an upper portion of the printer body while being guided by a paper guide (not shown). The driving shaft of the stepping motor 5 is extended in the axial direction, and its axial end is protruded on one side of the printer body 1. The axial end of the driving shaft is provided with a knob 7.
The knob 7 is manually turned outside the printer body 1, thereby rotating the driving shaft of the stepper motor 5. Consequently, the paper feeding roller 3 can be rotated through the deceleration gear system.
FIG. 6 depicts another type of conventional paper feeding system. A support shaft 8 is rotatably supported on one side portion of the stepper motor 5 in parallel with the driving shaft. One end of this support shaft 8 projects outside the printer 1, and the protruding end thereof is fitted with, a knob 7. The driving shaft of the stepper motor 5 is extends backwards. The rear end of this driving shaft and the other end of the support shaft 8 are provided with pulleys 9a and 9b, respectively. A belt 9c is stretched between the pulleys 9a and 9b. Based on this construction, the rotational force generated by manually operating the knob 7 is transferred via the belt/pulley mechanism 9 indirectly to the driving shaft.
As described above, in the conventional paper feeding mechanism the manual paper feeding operation involves the steps of rotating the knob 7, conveying the rotational force through the driving shaft of the stepper motor 5 to the deceleration gear system 6 and further rotating the paper feeding roller 3. By virtue of this manual paper feeding, there are effected positional adjustment to paper fed in and out of the printer.
The above-mentioned conventional paper feeding mechanism has, several defects. In both of the systems illustrated in FIGS. 5 and 6, the arrangement is such that the driving shaft of the stepper motor 5 is rotated by rotating the knob 7, and the rotational force is conveyed via the deceleration gear system 6 to the paper feeding roller 3. Hence, in the case of manually feeding the paper, if a deceleration ratio of the deceleration gear system 6 is set such as N=1/20, one rotation of the paper feeding roller 3 requires at least 20 rotations of the knob 7. The amount of paper fed is thus reduced, as compared with a frequency of rotation of the manual feeding knob 7. A large number of rotations of the knob 7 are needed for providing a required amount of paper feed.
In accordance with the prior art manual paper feeding system, in both cases shown in FIG. 5 and 6, the rotation of the knob 7 is transferred from the driving shaft of the motor 5 via the deceleration gear system 6 to the paper feeding roller 3. Therefore, where the deceleration ratio of the deceleration gear system 6 is large, it follows that a large force must be applied when the knob 7 is rotated. For this reason, the rotation can not easily be made by manual operation. As a result, it is quite difficult to perform the manual paper feeding because a large number of rotations must be done.
Besides, in the conventional paper feeding system, the rotational force is conveyed from the driving shaft of the stepper motor 5 via the deceleration gear system 6 to the paper feeding roller 3, at which time considerable deceleration is caused. Hence, the shaft must be extended long, and its end is fitted with the knob, or other special contrivances in order to cause rotations of the paper feeding roller 3 with no obstacle. For this reason, inexpensive motors available in the market can not to be used and particular specifications are required. This leads to greater cost than if commercially available ready-made motors could be utilized.